I've got two 730's but am unable to tell the channel capacity of each. It does have an eight pin chip, but no identification.
Also, I have two slightly different PLL boards, one will work down to 140 mhz or so, the other cannot be made to go below 146 mhz. I have taken pics if anyone has some thoughts on this. I would like to use them on Amateur bands as well as Public service. Thanks
TK-730 Channel and PLL Question
Moderator: willbartlett
Re: TK-730 Channel and PLL Question
I have had some success moving high split (146-174) TK-730's to work in all the ham band (144-148). The reason they squeal even tho using the "SP" function is that the VCO won't actually lock below 146 MHz.
It is gruesome, so is not for the faint of heart! What I determined from the schematic is that some capacitance had to be added to both the receive and transmit VCO's. In order to get to this board, you have to either remove the VCO cage (has 2 little holes in the top) and remove all the boards in that case, OR chop off the lid. The board in question is the one closest to the top of the stack, so I cut 3 sides of the lid with a dremel tool cut-off blade, bend it back and proceed to surgery.
I remove a 4pf capacitor from the transmit side, add it to the receive side, then put a 8.2 pf capacitor back where the 4 was. In most of the ones I have done, it ends up working from 140 to 163 MHz. I then tune the 4 front-end coils nearby for best sensitivity on 146.52 (seems to cover the 2 meter band well, as well as weather.)
DETAILS: On the VCO/PLL board, top layer: Remove C53. Move it to the junction of D55, L54, C61,/TC51, C62 and ground. (Basically, padding the coil L54.) I generally place it between the trace and the metal cage.)
Add a new 8.2 pf capacitor where the original C53 was. With the radio programmed to 146.52 and a signal generator into the antenna jack, tweek L4-L3-L2-L1 for best quieting. The sensitivity comes out to about .3-.4 microvolts or so.
I'll make an attempt to provide a picture if there is interest.
Daryl Duffin NU7X
nu7x@arrl.net
It is gruesome, so is not for the faint of heart! What I determined from the schematic is that some capacitance had to be added to both the receive and transmit VCO's. In order to get to this board, you have to either remove the VCO cage (has 2 little holes in the top) and remove all the boards in that case, OR chop off the lid. The board in question is the one closest to the top of the stack, so I cut 3 sides of the lid with a dremel tool cut-off blade, bend it back and proceed to surgery.
I remove a 4pf capacitor from the transmit side, add it to the receive side, then put a 8.2 pf capacitor back where the 4 was. In most of the ones I have done, it ends up working from 140 to 163 MHz. I then tune the 4 front-end coils nearby for best sensitivity on 146.52 (seems to cover the 2 meter band well, as well as weather.)
DETAILS: On the VCO/PLL board, top layer: Remove C53. Move it to the junction of D55, L54, C61,/TC51, C62 and ground. (Basically, padding the coil L54.) I generally place it between the trace and the metal cage.)
Add a new 8.2 pf capacitor where the original C53 was. With the radio programmed to 146.52 and a signal generator into the antenna jack, tweek L4-L3-L2-L1 for best quieting. The sensitivity comes out to about .3-.4 microvolts or so.
I'll make an attempt to provide a picture if there is interest.
Daryl Duffin NU7X
nu7x@arrl.net